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Foreword by Walter Cronkite  
Introduction - The National Science Foundation at 50: Where Discoveries Begin, by Rita Colwell  
Internet: Changing the Way we Communicate  
Advanced Materials: The Stuff Dreams are Made of  
Education: Lessons about Learning  
Manufacturing: The Forms of Things Unknown  
Arabidopsis: Map-makers of the Plant Kingdom  
Decision Sciences: How the Game is Played  
Visualization: A Way to See the Unseen  
Environment: Taking the Long View  
Astronomy: Exploring the Expanding Universe
Science on the Edge: Arctic and Antarctic Discoveries  
Disaster & Hazard Mitigation  
About the Photographs  
About the NSF  
Chapter Index  
Astronomy: Exploring the Expanding Universe

At the Center
of the Milky Way

Understanding the nature and appearance of our galaxy is no small feat, for we live within a disk of obscuring gas and dust.

Our sun is part of a large disk made up of stars and large clouds of molecular and atomic gas in motion around the Galaxy's center. Our solar system orbits this center, located about 30,000 light-years away from Earth, at 500,000 miles per hour. It takes our solar system 200 million years to make a single orbit of the galaxy.

The center of the Milky Way - click for detailsAstronomers can infer the shape and appearance of our galaxy from elaborate observations, and as a result have created maps of our galaxy. Yet parts of the Milky Way remain hidden-blocked by light-years of obscuring material (gas and dust) spread between the stars.

Andrea Ghez is working to penetrate the mysteries of this interstellar material. Ghez is an astronomer at the University of California at Los Angeles and an NSF Young Investigator, a national award given to outstanding faculty at the beginning of their careers. Her observations of the central regions of the Milky Way have permitted her to examine its very heart. Ghez, like many others, theorized that the Galaxy's core is the home of a supermassive black hole. "Although the notion has been around for more than two decades, it has been difficult to prove that [a black hole] exists," says Ghez. Now it appears her observations offer that proof.

Black hole at the center of our galaxy - click for detailsUsing one of the two W. M. Keck ten-meter telescopes on Mauna Kea in Hawaii, Ghez looked at the innermost regions of the Galaxy's core. For three years, she studied the motions of ninety stars. While scientists already knew that those stars nearest the center of the Galaxy move quickly in their orbits, Ghez was astonished to discover that the stars nearest the center of the Milky Way were moving at speeds as high as three million miles per hour. Only a very large assembly of superconcentrated mass inside the stars' orbits could whip them around at those speeds. "The high density we observe at the very center of the Milky Way exceeds that inferred for any other galaxy, and leads us to conclude that our galaxy harbors a black hole with a mass 2.6 million times that of the Sun," Ghez notes.

Astronomers do not think that a supermassive black hole at the center of a galaxy is unique to the Milky Way. Rather, it appears to be quite typical of the almost innumerable galaxies in the observable universe. The fact that black holes may be the rule rather than the exception makes it even more important that we continue to study them.

PDF Version
Voyage to the Center of the Sun
New Tools, New Discoveries
At the Center of the Milky Way
The Origins of the Universe
The Hunt for Dark Matter
Shedding Light on Cosmic Voids
Visualizing the Big Picture
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